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View Full Version : Set in place material for Fabrications??



Mcgyver
12-18-2010, 11:22 AM
Lousy title, wasn't sure how to describe the need.....

Picture some rectangular structural steel that has to have a jack shaft go through it and will have ball bearings in holders (I'll turn) bolted to the structural steel. The problem is i can't rely on the surface of the steel to be flat and parallel enough so that things won't bind when its tightened up. On of the bearing housings is going on the inside so that eliminates take a pass with a fly cutter.....which I'm reluctant to do anyway as it can cause warping etc.

What I'm looking for is something that i can put a thin coat of on between the housings and the structural steel so that i can get it all place with the shaft but not tighten anything.....then let it set up using the shaft for alignment sort of like you'd use moglice on a carriage after grinding. (but cheaper than that!)

would this JB weld stuff do? never used it, or is there another product that comes to mind?

thanks

lazlo
12-18-2010, 11:35 AM
JB Weld is just a metal-filled epoxy, so whether it would work is entirely constrained by the load it will be subjected to.

What about bolting the bearing blocks to the structural beams with 3- or 4-point height adjusters. Put a jam nut on each (like the adjustment block on a bandsaw freewheel), and you can set the height/offset and a compound angle.

Barrington
12-18-2010, 11:35 AM
Sounds difficult to achieve. How about :-

e.g. Self_Aligning_Ball_Bearing (http://www.bearingboys.co.uk/Self_Aligning_Ball_Bearing-1015-c?gclid=CL670s2d9qUCFQ8f4QodvkCQpA)

Cheers

.

Rustybolt
12-18-2010, 11:37 AM
A sketch would help, and some idea of how big this thing is.

"Precison" and "Structural Steel" should never be combined unless you like pain. Just plain hot rolled should be in there too.

strokersix
12-18-2010, 11:44 AM
You need mounted bearings. There are pillow block style and flange style. The bearing element is mounted inside a spherical cavity in the casting for just this purpose. Drill some holes and bolt the flange wherever you wish.

mochinist
12-18-2010, 11:50 AM
Its not cheap, but it works great

Its like JB weld that ate steroids
http://www.belzona.com/prod1k.aspx

I use the 1111 formula for some quick repairs

RussZHC
12-18-2010, 11:58 AM
don't know that it would be a lot different than JB but I think of "Devcon" (or whatever the corp name is by now) and they even list a "case study" with some similarities.

http://www.devcon.com/products/products.cfm?csid=109&family=Plastic%20Steel%C2%AE%20Putty%20%28A%29&brand=Devcon

a number of their products talk about use "encapsulating" which maybe of use for that internal mount...

wierdscience
12-18-2010, 01:53 PM
Simple,paper towel paper "gaskets" soaked in Loctite 271.Install wet,snug the screws,wait till cured and then tighten.

Either that or use spherical OD bearings and turn up some housings for them.

DICKEYBIRD
12-18-2010, 02:20 PM
I'm in the process of doing a similar job myself, if I'm picturing yours properly.

I'm fitting 2 steel bearing mount plates at either end of a piece of 3" square, 1/4" wall tubing. My plan is to skin the inner surfaces to clean them up & remove the weld seam, press fit the plates and drill/tap through the corners for allen screws. The plates will be doused in Loctite 680 before they're bolted up.

My plan is to then line bore for the bearings after it's cured with the assembly bolted onto the lathe carriage. We'll see how it goes after the holidays. All I can do now is dream about shop work. Gotta overhaul the house for a big (22 people) Christmas dinner.:eek:

TGTool
12-18-2010, 06:15 PM
I encountered a guy who has a business building special machines of all kinds. He makes just wonderful structures utilizing mostly tubing, welded up and stress relieved. All ends are capped and welded for rigidity making sure each cavity has at least one vent for pressure during the heat treat. Any place there's something mounted, such as a slide bearing, he mills out a small section of tube and then welds in a rectangular steel chunk that can be finish machined to dimension. If there are serious fasteners going through both sides of a tube, he'll drill through so a heavier wall transverse round tube can be welded in both sides to avoid any crushing, deforming, or loss of tension on the fasteners. I wish I had pictures of some of his stuff because it's a real treat to see his finished work.

Robin R
12-18-2010, 06:39 PM
A sketch of what you are building would be helpful, as your description is a bit open to interpretation. It sounds like you are going to run the shaft through opposite sides of some square tubing, with one of the bearings on an inside face. I believe you have a shaper, so couldn't you make a light cleanup pass, using a boring bar in the shaper.

darryl
12-18-2010, 06:55 PM
Any decent grade of filled epoxy should do the job. One of the benefits of using epoxy is that it will occupy all the space between parts and therefore support the part over the largest area possible. This avoids distortion of the part, such as an outer bearing race where you definitely want it to remain round. It will also result in maintaining the load bearing capacity of the bearing. There are a couple caveats of course (or is that curse)- the filler material has to actually fill and not leave unseen air pockets. It's usually best to wipe a coat of epoxy on both mating surfaces, then clean up the squirtout after the fact. You don't want to end up with parts glued together where there is supposed to be relative motion. Then of course, the parts are generally not separable after being epoxied. If you need to be able to replace a bearing, you'll have to think about how this can be done in future.

The assembly process has to be designed to cater to the final alignment and epoxying. I've done projects where there's bolts holding pieces together and epoxy filling the voids. Where there's an alignment issue, the bolts are used to bring the parts together, but aren't tightened fully until the epoxy has set. This allows the setup to self-align and cure that way, then the bolts are tightened to keep the parts together. The epoxy is not relied upon to do that, and therefore is acting mostly as a filler. Under those circumstances, there's no compromise in strength or structural integrity of the assembly.

JB weld would be fine- my preference is PC-7, both because I have some, and because I've proven its worthiness. It's not runny, in fact it's quite stiff, so as a filler it's best when parts come together 'on the flat'. If gluing a bearing race into a cavity, a runnier epoxy might be better. JB is runnier than PC-7.

Whatever you use, it should not have additives that dissipate and allow the material to shrink. There was talk of this on the polymer concrete thread, which discussed epoxy granite and the use of proper compounds that don't shrink. I don't think JB or PC-7 have this problem. I'd avoid fast cure and really fluid epoxy concoctions.

Mcgyver
12-18-2010, 11:28 PM
thanks for all the great ideas! Forces are 99% radial (jack shaft on my cnc servo upgrade) and bearing housings will sit in holes bored in the tubing.....so loads will all be shaft -> bearing -> housing -> structure. The cast in-place bit ensures alignment. Things are tight, not much room for self aligning bearings etc....I'd make it like a spindle with its own end to end housing but its more material/work and I want to mount a timing belt pulley between the bearings. results to follow and a sketch if i can ever get it done in a semi readable format :)